diff options
| -rw-r--r-- | Documentation/filesystems/proc.txt | 18 | ||||
| -rw-r--r-- | fs/proc/array.c | 123 | ||||
| -rw-r--r-- | fs/proc/base.c | 3 | ||||
| -rw-r--r-- | fs/proc/internal.h | 1 |
4 files changed, 145 insertions, 0 deletions
diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt index 912af6ce562..d8d3f9a8e5a 100644 --- a/Documentation/filesystems/proc.txt +++ b/Documentation/filesystems/proc.txt @@ -40,6 +40,7 @@ Table of Contents 3.4 /proc/<pid>/coredump_filter - Core dump filtering settings 3.5 /proc/<pid>/mountinfo - Information about mounts 3.6 /proc/<pid>/comm & /proc/<pid>/task/<tid>/comm + 3.7 /proc/<pid>/task/<tid>/children - Information about task children 4 Configuring procfs 4.1 Mount options @@ -1578,6 +1579,23 @@ then the kernel's TASK_COMM_LEN (currently 16 chars) will result in a truncated comm value. +3.7 /proc/<pid>/task/<tid>/children - Information about task children +------------------------------------------------------------------------- +This file provides a fast way to retrieve first level children pids +of a task pointed by <pid>/<tid> pair. The format is a space separated +stream of pids. + +Note the "first level" here -- if a child has own children they will +not be listed here, one needs to read /proc/<children-pid>/task/<tid>/children +to obtain the descendants. + +Since this interface is intended to be fast and cheap it doesn't +guarantee to provide precise results and some children might be +skipped, especially if they've exited right after we printed their +pids, so one need to either stop or freeze processes being inspected +if precise results are needed. + + ------------------------------------------------------------------------------ Configuring procfs ------------------------------------------------------------------------------ diff --git a/fs/proc/array.c b/fs/proc/array.c index 3a26d23420c..62887e39a2d 100644 --- a/fs/proc/array.c +++ b/fs/proc/array.c @@ -565,3 +565,126 @@ int proc_pid_statm(struct seq_file *m, struct pid_namespace *ns, return 0; } + +#ifdef CONFIG_CHECKPOINT_RESTORE +static struct pid * +get_children_pid(struct inode *inode, struct pid *pid_prev, loff_t pos) +{ + struct task_struct *start, *task; + struct pid *pid = NULL; + + read_lock(&tasklist_lock); + + start = pid_task(proc_pid(inode), PIDTYPE_PID); + if (!start) + goto out; + + /* + * Lets try to continue searching first, this gives + * us significant speedup on children-rich processes. + */ + if (pid_prev) { + task = pid_task(pid_prev, PIDTYPE_PID); + if (task && task->real_parent == start && + !(list_empty(&task->sibling))) { + if (list_is_last(&task->sibling, &start->children)) + goto out; + task = list_first_entry(&task->sibling, + struct task_struct, sibling); + pid = get_pid(task_pid(task)); + goto out; + } + } + + /* + * Slow search case. + * + * We might miss some children here if children + * are exited while we were not holding the lock, + * but it was never promised to be accurate that + * much. + * + * "Just suppose that the parent sleeps, but N children + * exit after we printed their tids. Now the slow paths + * skips N extra children, we miss N tasks." (c) + * + * So one need to stop or freeze the leader and all + * its children to get a precise result. + */ + list_for_each_entry(task, &start->children, sibling) { + if (pos-- == 0) { + pid = get_pid(task_pid(task)); + break; + } + } + +out: + read_unlock(&tasklist_lock); + return pid; +} + +static int children_seq_show(struct seq_file *seq, void *v) +{ + struct inode *inode = seq->private; + pid_t pid; + + pid = pid_nr_ns(v, inode->i_sb->s_fs_info); + return seq_printf(seq, "%d ", pid); +} + +static void *children_seq_start(struct seq_file *seq, loff_t *pos) +{ + return get_children_pid(seq->private, NULL, *pos); +} + +static void *children_seq_next(struct seq_file *seq, void *v, loff_t *pos) +{ + struct pid *pid; + + pid = get_children_pid(seq->private, v, *pos + 1); + put_pid(v); + + ++*pos; + return pid; +} + +static void children_seq_stop(struct seq_file *seq, void *v) +{ + put_pid(v); +} + +static const struct seq_operations children_seq_ops = { + .start = children_seq_start, + .next = children_seq_next, + .stop = children_seq_stop, + .show = children_seq_show, +}; + +static int children_seq_open(struct inode *inode, struct file *file) +{ + struct seq_file *m; + int ret; + + ret = seq_open(file, &children_seq_ops); + if (ret) + return ret; + + m = file->private_data; + m->private = inode; + + return ret; +} + +int children_seq_release(struct inode *inode, struct file *file) +{ + seq_release(inode, file); + return 0; +} + +const struct file_operations proc_tid_children_operations = { + .open = children_seq_open, + .read = seq_read, + .llseek = seq_lseek, + .release = children_seq_release, +}; +#endif /* CONFIG_CHECKPOINT_RESTORE */ diff --git a/fs/proc/base.c b/fs/proc/base.c index bd8b4ca6a61..616f41a7cde 100644 --- a/fs/proc/base.c +++ b/fs/proc/base.c @@ -3400,6 +3400,9 @@ static const struct pid_entry tid_base_stuff[] = { ONE("stat", S_IRUGO, proc_tid_stat), ONE("statm", S_IRUGO, proc_pid_statm), REG("maps", S_IRUGO, proc_tid_maps_operations), +#ifdef CONFIG_CHECKPOINT_RESTORE + REG("children", S_IRUGO, proc_tid_children_operations), +#endif #ifdef CONFIG_NUMA REG("numa_maps", S_IRUGO, proc_tid_numa_maps_operations), #endif diff --git a/fs/proc/internal.h b/fs/proc/internal.h index a30643784db..eca4aca5b6e 100644 --- a/fs/proc/internal.h +++ b/fs/proc/internal.h @@ -54,6 +54,7 @@ extern int proc_pid_statm(struct seq_file *m, struct pid_namespace *ns, struct pid *pid, struct task_struct *task); extern loff_t mem_lseek(struct file *file, loff_t offset, int orig); +extern const struct file_operations proc_tid_children_operations; extern const struct file_operations proc_pid_maps_operations; extern const struct file_operations proc_tid_maps_operations; extern const struct file_operations proc_pid_numa_maps_operations; |